The mechanisms regulating the 4-10 fold reduced accumulation of ribosomes following the fusion of mouse myoblasts into muscle fibers will be examined. Specifically, the role of r-protein synthesis and degradation in regulating the reduced accumulation of r-proteins following myoblast fusion will be determined in pulse chase experiments. The mechanisms regulating the synthesis of r-proteins in myoblasts and fibers will be determined from measurements of r-proteins mRNA concentrations, transcription rates and stabilitites using RNA-DNA hybridization techniques. Possible differential expression of members of an r-protein gene family during muscle development will also be examined using molecular cloning and hybridization techniques. Further, the role of rRNA transcription and the role of degradation if pre-rRNAs during processing in regulating the reduced formation of rRNA in fibers will be determined and points during processing that degradation of pre-rRNAs can occur will be identified.